1. Field of the Invention
The present invention relates to aquarium filter, in particular to aquarium filter provided with a pump. The invention also relates to the use of such a device in combination with a suction attachment for cleaning purposes.
2. Description of the Related Art
An aquarium is a small, closed underwater biotope. At first glance the life in an aquarium consists of fish and plants, but as in every biotope, balance cannot exist in the absence of bacteria. Among other things, bacteria are necessary for processing waste materials in the aquarium and are also called nitrifying bacteria. These bacteria process the waste materials in the aquarium in several steps to form the relatively harmless nitrate. This process is also known as the nitrogen cycle.
The first step consists of the breakdown of large molecules, resulting in the production of molecular ammonium. This is done by bacteria (but not nitrifying ones) that are present in the environment and are not attached to a carrier. They occur floating freely in the water and on the bottom, or fact, wherever waste is present and are known as detritivores.
Simply stated, detritivores break down starches, proteins and fats, in other words they take care of the first breakdown of all the vegetable and animal material. To use more technical terms, they have amylolytic (starch-degrading), proteolytic (protein-splitting) and lipolytic (release of fatty acids from fat storage) activity. Thus they perform the preparatory work for nitrification and make possible further breakdown by the bacteria in the filters. The larger debris is their food, and their waste products are the simplified molecules, such as ammonium/ammonia, which in turn serve as food for the nitrifying bacteria. In contrast to the detritivores, nitrifying bacteria must attach to a carrier. For this reason, the substrate used for filters is very important.
The so-called nitrosomonas bacteria are responsible for the second part of the nitrogen cycle. They convert the waste materials in the aquarium from ammonium via ammonia to nitrite, which is harmful even in small quantities. In a well-functioning aquarium the nitrite levels should not rise high too rapidly, since the nitrite is almost immediately converted to the (practically) harmless nitrate (NO3). The latter is done by the so-called nitrobacter bacteria. Both of these bacteria are from the aerobic bacteria family. Nitrate is harmful to fish only at very high concentrations of more than 100 mg/l. In the aquarium in general the nitrogen cycle will stop at this point, but in reality the nitrogen cycle is not yet complete. In nature, nitrate is converted into the gases nitrogen (N2) and oxygen (O2). These gases rise out of the water and the nitrogen cycle is then complete. Since the bacteria that perform this last step live under anaerobic conditions, these (anaerobic) bacteria are found at the bottom or in the bed of the aquarium. The bed has the advantage that, here, non-moving, low-oxygen water is present between the gravel pieces. In order to improve the conditions still further, pieces of lava stone (lava granules) may be first place on the bottom and then covered with gravel. The porous structure of the lava stone provides a much larger surface area and the anaerobic bacteria can nestle better into the lava stone. They can also multiply better there than in gravel.
In a newly established aquarium the equilibrium between the above-mentioned nitrosomonas and the nitrobacter bacteria may not be well-balanced. This is because the nitrosomonas bacteria multiply more rapidly than the nitrobacter bacteria. If a large amount of waste material suddenly enters the aquarium, not enough nitrobacter bacteria will be present to be able to process the nitrite suddenly formed in the aquarium, and thus nitrite problems will occur. Table 1 below shows what a certain nitrite value means for the aquarium.
TABLE 1Nitrite value (in mg/l)Significance for the aquarium<0.1Causes no problems in the aquarium0.2Nitrite value is toxic for the fish0.5Nitrite value is a cause for concern2.0Lethal for fish
Although strictly speaking a nitrite value of 2.0 mg/l is lethal to fish, a lower value can also cause death of fish. This is because a nitrite value of 0.2 mg/l or higher is already toxic for fish. As a result, the fish will become more susceptible to diseases and thus die indirectly as a result of the nitrite. Likewise the sensitivity to nitrite differs according to the fish species. Thus the values above cannot be regarded as definite values.
A number of measures that can help manage the nitrite content in the aquarium include:                Feeding in moderation. The food that is not consumed will rot in the aquarium and thus can result in excessively high nitrogen contents.        Provision of a good filter. A good filter can ensure that the nitrite content does not become too high. Specifically, a large number of bacteria deposit quickly on the substrate in the filter, since a lot of food is present here and also a lot of oxygen. A good interior filter within the aquarium may be adequate for an aquarium that is not too large. An external filter can have a larger filter volume and it is often easier to change the types of substrate to one on which bacteria more readily settle.        Plants ensure rapid stabilization of the aquarium. Therefore it is sensible to plant a number of strong, healthy growing plants in the aquarium. Bacteria also attach to plants, and plants are naturally also appealing to the eye.        Commercially available bacteria may be added to the water. Various agents containing suitable bacteria can be purchased for use in setting up a new aquarium.        Changing too much water at once can lose part of the bacterial culture. Therefore it is not good to replace too much water or replace it too frequently. To reduce the quantity of waste materials, weekly replacement of a maximum of ¼ of the aquarium water is advisable. But this should definitely not be done more than once a week. After starting a new aquarium one should wait at least about 3 weeks before changing the water for the first time so as not to interfere with the growth of bacteria.        Avoid too many fish in the aquarium, since the more fish are in the aquarium, the more waste materials will enter the aquarium. A densely populated aquarium will develop a nitrite problem sooner than a sparsely populated one.        The bacterial count depends on the food supply. Thus when many fish are simultaneously released into an aquarium, initially there will be a shortage of nitrobacter bacteria to process the suddenly large supply of waste, and there is a great chance of a high nitrite value. By placing fish in the aquarium progressively the bacterial colony can be allowed to grow gradually and the formation of nitrite will be prevented.        
Despite taking these precautions, maintaining a healthy aquarium is difficult and requires considerable care and attention. Water and bottom fouling of the aquarium requires considerable effort to keep clean. Especially bottom fouling is inconvenient, since it requires direct attention e.g. using a suction/vacuum attachment. A particular burden is the need for regular cleaning of the conventional cartridge filter, which is necessary since otherwise water values may begin to vary after 6 to 8 weeks. Stinking detritus consisting of accumulating fish faeces, sludge, leftover food and plant residues will be familiar to anyone that has performed this task. The result is almost always floating debris that drifts around in the water in the aquarium and greatly reduces viewing pleasure. With a cichlid aquarium the experienced aquarist understands that the debris levels will be somewhat higher than in other aquaria and it can be necessary to changes 25/30% of the water per week to keep the aquarium clean and clear.
It would be desirable to provide a filter that was able to overcome at least some of the above-mentioned inconveniences.